Preparation of surface-active agents



United States Patent 3,394,155 PREPARATION OF SURFACE-ACTIVE AGENTS Arno Cahn, Pearl River, N.Y., and Henry Lemaire, Leonia, N.J., assignors to Lever Brothers Company, New York, N.Y., a corporation of Maine No Drawing. Filed May 22, 1%4, Ser. No. 369,597 Claims. (Cl. 260-400) ABSTRACT OF THE DISCLGSURE This application discloses a method for preparing esters of predominantly coco fatty acid and a hydroxy sulfonate by direct esterification which minimizes the residues of unreacted fatty acids of C C canbon chain lengths. This as achieved by adding the fatty acid reactant in two steps. In the first step typically coco fatty acids, containing substantial quantities of the C -C fatty acids, are added in a quantity sufficient to provide the desired proportion of coco esters in the final product, but insufiicient to completely consume the hydroxy sulfonate. In the second step sufficient additional fatty acid is added to provide a high conversion of the hydroxy sulfonate, the additional fatty acid, however, containing substantially lower proportions of the C3-C1Z fatty acids.

The present invention relates to the preparation of surface-active agents. More particularly, it relates to a process for preparing surface-active agents of the general formula RCOORSO M, where R is a monovalent aliphatic hydrocarbon radical having from 7 to 19 carbon atoms, R is selected from the group consisting of divalent aliphatic hydrocarbon radicals containing from 2 to 4 carbon atoms and aryl and alkyl-aryl radicals containing from 6 to 8 carbon atoms, and M is an alkali metal cation, the surface-active agents being prepared by the direct esterification of the corresponding hydroxy-sulfonatc.

The direct esterification of the hydroxy-sulfonates with an organic acid may be advantageously carried out in the presence of a reaction promoter, i.e., compounds which promote a high conversion of the hydroxy-sulfonate to the corresponding ester. It should be understood, however, that the present invention is not concerned with reaction promoters. While the inventive concept of the present invention may be practiced Without employing them, for commercial purposes it is usually preferred that they be used. Compounds having this effect include, but are not limited to, salts of strong acids and weak bases such as stannous sulfate, titanium sulfate, cadmium sulfate, tungsten phosphate; acids or acid formers such as chloroacetic acid, ethyl chloroformate, coconut fatty acid chloride, boric acid, para-toluene sulfonic acid; neutral or basic compounds such as cerium oxide, lanthanum oxide, didymium oxide, zinc oxide and zinc soaps, magnesium oxide and magnesium soaps.

In carrying out this reaction, the organic acids which are suitable for the manufacture of surface-active agents may be used. In general, these are the carboxylic acids of aliphatic hydrocarbons having from 8 to 20 carbon atoms. Such acids include the unsubstituted, saturated or unsaturated, straight-chain, fatty acids, such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, stearolic acid, acids derived from bone grease (a mixture of C fatty acids), acids derived from palm kernel oil (a mixture of C fatty acids), and acids derived from coconut oil (a mixture of C fatty acids), and acids derived from tallow (a mixture of saturated and unsaturated C fatty acids). Synthetic acids such as those derived from the 0x0 and Koch processes may also be used. Aliphatic acids of the foregoing types may be used pure or may be employed as mixtures. For preparing surface-active agents, the foregoing acids should be selected so that the ultimate product will contain a major portion of C C fatty acid esters. This will normally require the use of acids having at least about 40% of the C C fatty acids.

As compounds of the formula HORSO M (hereinafter also referred to as the second reactant) it is pre ferred to use a compound in which R is a divalent hydrocarbon radical containing 2 to 4 carbon atoms, particularly ethylene, methylethylene, dimethylethylene, propylene or butylene. R may also be an aryl or alkyl-aryl group containing from 6 to 8 carbon atoms. M is preferably an alkali metal (e.g. lithium, sodium, potassium, rubidium and calcium), especially sodium or potassium. The preferred second reactant may be prepared by the reaction of an epoxide, for example ethylene oxide, propylene oxide or butylene oxide, with sodium bisulfite. Examples of compounds suitable for use as the second reactant are sodium isethionate, potassium methyl isethionate, sodium dimethyl isethionate and sodium 3-hydroxypropane-sulfonate.

In order to achieve a high utilization of the hydroxysulfonate, the reaction is normally carried out using an excess of the acid reactant. In general, at least 1.2 moles of acid per mole of hydroxy-sulfonate are employed, and the amount of excess acid may exceed 2. moles per mole. The excess acid, in addition to producing a high utilization of the hydroxy-sulfonate, assists in maintaining the product in liquid form during the reaction and in reducing formation of foam. As a result of the foregoing, the reaction product contains significant amounts of free acid reactant.

The products of the reaction are generally used as detergents, such as in the manufacture of detergent tablets or the manufacture of detergent hand soaps in bar form. For this purpose, it is usually desirable to reduce the amount of free fatty acids of lower molecular weight in the reaction product (e.g. the C C acids). The acids of lower molecular weight adversely affect the qualities of the detergent products. The presence of the lower molecular weight fatty acids containing up to 10 carbon atoms is particularly undesirable from the standpoint of odor. These same acids are also irritating and are therefore undesirable when used in hand soap bars or other applications where mildness to the skin is desirable. The C3-C12 fatty acids are undesirable because they adversely affect the plodding characteristics of the finished product. While the removal of excess free acid reactant by distillation or by neutralization is known, such processes have the disadvantage of introducing extra processing steps, or of introducing neutralization products, e.g., sodium soaps, which are not necessarily desirable.

According to the persent invention, it has been discovered that acyl hydroxy-sulfonate esters of the formula RCOOR'SO M can be produced directly, containing acceptably small residues of unreacted acids of low molecular weight, by adding in successive steps two aliphatic acid reactants of the formula RCOOH.

In the first step, the acid which is to form the major portion of the ester is reacted with the hydroxy-sulfonate. This first acid includes C to C aliphatic acids of the formula RCOOH but may contain acids having from about 8 to about 20 carbon atoms. Coconut fatty acids are typical of the commercially useful fatty acids which may be used as the first acid. The coconut fatty acids contain predominantly C to C fatty acids and contain in excess of C3 to C12 acids.

Generally, about 0.8 to about 1.1 moles of the first acid per mole of hydroxy-sulfonate are employed. The reaction is allowed to proceed to substantial completion. Usually a period of 2565 minutes is sufficient for this purpose.

' While the cessation of water evolution may be used as a convenient indication of the completion of the reaction, it is preferred not to let the esterification reaction cease since it is difficult to restart this reaction. In the preferred process, the reaction is allowed to proceed, after the addition of the first portion of the acid, for a period of 30 to 50 minutes at the reaction temperature. At the end of this period the first step in the preferred embodiment of the reaction will be substantially complete, although the esterification reaction will not have ceased.

After the first step of the reaction has been completed, or after the expiration of the allotted time therefor, a second aliphatic acid of higher molecular weight is added, and the reaction allowed to proceed to substantial completion. Aliphatic acids suitable for use in this second step are of the formula RCOOH, and consist essentially of C to C acids. Talow fatty acids are typical of those which may be used.

The amount of the second acid which is added should be sufficient so that the total amount of the first and second acid reactants is at least about 1.2 moles of acid per mole of hydroxy-sulfonate. This ratio will provide for a high uilization of the hydroXy-sulfonate. In addition it will maintain the fluidity of the reaction system and will reduce the foaminess thereof as discussed above.

The reaction in each step is carried out at a temperature sufficient to result in a completed reaction in a reasonable time. Typically, in the absence of a reaction promoter, a temperature of about 200 to about 250 C. will be required. However, if a reaction promoter is employed, the maximum reaction temperature need not exceed about 240 C.

When the direct esterification raction is carried out in two steps, as described above, the amount of the fatty 3 acid added during the first step is sufficient to react with approximately 60%-80% of the hydroxy sulfonate present, yielding an initial reaction product containing from 50% to 60% ester, to free fatty acid, and 15% to 20% unreacted hydroxy-sulfonate. The amount of uncombined lower molecular weight fatty acids will depend on the proportion of such acids in the acid reactant. If coconut fatty acids are employed as the reactant, these will typically be in the order of 12%15% uncombined lower molecular Weight acids.

The addition of the second higher molecular weight fatty acid, causes the reaction to continue further toward completion, in accordance with the governing equilibria, and will produce a conversion of hydroxy-sulfonate to the corresponding ester in the order of 90%95%. During the continuance of the second step in the reaction, the first and second fatty acids are consumed at relative rates which are in substantially the same proportion to each other as the relative concentration of these acids present. Accordingly, an additional portion of unreacted fatty acid remaining from the first step .of the reaction, normally about 30%35% thereof, is converted to the corresponding ester. The resulting product will contain a lower concentration of unreacted lower molecular weight fatty acid than would have resulted if the conventional, single-step process, had been employed. For instance, if coconut fatty acids and tallow fatty acids are used, as described above, in two successive steps, the resulting product will contain .in the order of 0.080.11 part of unreacted lower molecular weight fatty acids (per part of acyl hydroxy sulfonate), while had a sufiicient amount of coconut fatty acids been employed to complete the reaction in a single step, the product would contain about 0.100.l7 part of free lower molecular weight fatty acids. This reduction in the concentration of free lower molecular fatty acids will provide a significant improvement in the properties of a detergent bar containing acyl hydroxy-sulfonates. Acyl hydroxy-sulfonates containing 0.14 part by weight of free lower molecular weight fatty acids would not be suitable for use directly in detergent bars; however, the material containing up to about 0.1l part by weight of free fatty acid may be used directly without further purification.

While the present invention is particularly applicable to acyl hydroxysulfonates prepared by direct esterification employing fatty acids containings in excess of 40% C -C fatty acids, it is not to be so limited. Even when employing fatty acids containing a sufficiently low concentration of C C fatty acids that objectionable residues do not remain, an improvement in properties may be obtained by the practice of the present invention.

For a better understanding of the present invention reference may be had to the following examples.

EXAMPLE 1 The following test was performed to illustrate a typical application of the step-wise addition of fatty acid reactants according to the present invention.

A mixture of 18 gms. of sodium isethionate (0.8 mole) and gms. (0.915 mole) of coconut fatty acid, designated as fatty acid 1, was charged to a one-liter reactor, stirred, and covered with nitrogen. The sodium isethionate was added as a simulated aqueous slurry such as would be encountered in commercial production.

One-half liter per minute of pre-purified nitrogen containing approximately 8 parts per million of oxygen was bubbled through the reaction mixture, and withdrawn from the reaction vessel through a water condenser and a dry ice condenser. Zinc oxide (3.74 gms.) was added with the initial charge.

The reactor was heated on an oil bath to 230 C., all of the initial water being removed during the heating period. The reaction temperature of 230 C. was maintained for 40 minutes.

A small sample of the reaction melt was taken at this point, and the amount of coconut-isethionate produced was determined by a Hyamiine titration (described in ASTM Standards, Part 10, 1961, pages 1099-1101) using diphenyl isobutylphenoxyethoxyethyl dirnethyl benzyl ammonium chloride dihydrate. Based on the amount of coconut-isethionate produced, the composition of the reaction product at the termination of the initial step is calculated as follows:

TABLE I First Product (304 gms. 68.6%

Initial Charge active, 208.5 gms.

A second portion of 30 gms. of fatty acid, designated as fatty acid 2, was thereupon added to the reaction mass at the termination of the first reaction. In this illustrative example, coconut fatty acid was used as fatty acid 2 to simplify the calculations. A higher weight molecular fatty acid, such as stearic acid would normally be used in its place, and would be equivalent in all respects. The reaction was continued at 230 C. until water evolution ceased, indicating the end of the reaction. The termination of the reaction was verified by continuing the heating and stirring for an additional 10 minutes after cessation of water evolution.

A sample of the second reaction mass was taken and the total amount of coconut-isethionate produced was again determined by the Hyam'ine titration. Based on this determination, calculations were made to estimate the additional amount of fatty acid 1 remaining from the first step which reacted during the second step, and the amount of fatty acid 2 which reacted. The results are set forth in Table 11.

5 6 TABLE II EXAMPLE 5 Subsequent To further illustrate this invention, a direct esterifica- Charge actflvei 262 gms. tion reaction was carried out and a detalled analysis of atty acidisethionate) 5 the reaction products was made. The reaction was carried 8E5. Moles Gms. Moles out as 9 S d. m t 5 03 A mixture of 98 gms. of hardened coconut fatty aclds l m 1 8 10 ll e 1 3a; 1101 111 58% 0 -012 acids) 42.5 0.20 (0.46 mole), 59 gms. of sodium isethionate (0.40 mole), Fatty 801d 30 2 gms. of Zinc oxide, and gms. of water was stirred Fatty acid-1seth1onatc 1 245 0. 715 Fatty acid-isethionate2 17 0. 05 10 whlle nitrogen was passed through the melt, fOllOWlHg Total yield of fatty acid-isethionates (94% of the acyl isethionate yield geflerany the procedure outhnefi m Example above T is formed from fatty acid 1) =95%. mixture was heated to 221 C. 1n about 45 minutes during Total fre tty ac d (parts by weight) whlch time most of the watenadded to the charge was Tot y acldlsethlonate driven off and collected. Heating was continued for an Tltrelefiicngat itrtac st :009 (parts by weight). additional /2 hr., the temperature being maintained be- 0 a a Yam e tween 226 and 232 0, although near the end of this period the temperature rose to 237 C. and the reaction vessel became filled with foam. Preheated Emersol 132, thg foregoingreactlofl W111 be noted that gross 20 a mixture of 45% stearic acid and 55% palmitic acid (26 ratio of coconut fatty acid added as the first portion to gms. 0'097 mole) was added and the reaction continued sodium isethionate is 1.14:1 mole per mole. Because the for an additional hour catalyst used was zinc oxide, a portion of the fatty ac1d A Hyamine titration of a sample of the hot residue reactant was ccfnslmfed saPomfl/mgthe Zmc showed a conversion of 94.5% based on the weight of correspondmg Z111? Soap; Accordmgly, h efiecjuve the isethionate. Thus, the hot residue of 173 gms, con- 0f fatty acld avallable to react wlth Sodlum tained 131.5 gms. of acyl isethionates, 3 gms. of unreacted lset w 1S moles P sodium isethionate, 2 gms. of ZnO (probably present as a fatty acid salt) and 36.5 gms. of free fatty acids. EXAMPLES 2-4 The acyl isethionate product and the free fatty acids 30 were analyzed by gas-liquid chromatography. The results The procedure outlined in Example 1 Was p a e f r of this analysis are shown in Table VI (columns 2 and 5). several other illustrative conditions. The results of these The roportions of the acyl isethionate and free fatty tests are set forth in Tables III, IV and V. acids derived respectively from the coconut fatty acids (CNFA) and Emersol 132 may be computed from these analyses. Since the Emersol 132 contained no C to C fatty acids, the amounts of these radicals appearing in TABLE III-REACTION YIELDS the product may be assigned to the coconut fatty acids. lgolgrtltgio %IF1attyf' The amounts of C to C acids associated with the coco- Gl 0 1'18 080 Example Sodium Isethionate 2110, Percent Percent nut fatty acid and the Emersol 4 respectlvely y be Fm Acidl Fatty e Actlve COHWISIOII computed based on the known distribution of fatty acids (56%yCrgn) A idg a in these acids. As indicated in Table VI (columns 3, 4, 6 1.14 0.18 3H 77 go and 7), this computation shows that approximately 84% b 1.14 0.18 3.0 d 79 93 r of the acyl isethionate was derived from the coconut fatty 19 3 74 76 9 acids and approximately 74% of the free fatty acids were Coconut fatty acid in Examples 2 and 3. In Example 4 a micture of d i d f o th o ut f tt id Th th fi i h d steam: and 55% palmitic acids was used.

Corrected ratio, 1.05; 1. product contains approximately 0.08 part of uncombmed ig i g g g fg gg ggg ig figff Ramon of fatty and lower molecular weight fatty acids per part of acyl isethid By Hyamine titration, molecular weight of product assumed to be onate product and approximately 0.28 part Of total fatty acids per part of acyl isethionate product. Had only coconut fatty acids been employed as the fatty acid reactant, the resulting product would have contained about 0.15 TABLE IV-"REACTION CONDITIONS part of uncombined lower molecular weight fatty acids. Fatty Acidl Fatty Acid2 This reduction in the amounts of uncombined lower (56% CFC) molecular weight fatty acids provides a significant im- E m E u g gag $3 511 provement in the properties of the finished product and m avoids the necessity of a subsequent distillation step which 2g 338 2 would otherwise be required to reduce the amounts of un- 25 230 50 231 60 reacted lower molecular weight fatty acids to acceptable 1 See footnote at end of Table V. levels TABLE V.PRODUCI COMPOSITIONS (l -C12 Total Fatty Fatty Acid- Fatty Acid Ex. Fatty Acids Acids l Isethionate 1 Isethionate 2 1 Girls. Ratio Gms. Ratio Gms. Moles Gms. Moles 2s 0. 11 72 0. 29 232 0. 675 13 .04 2e 0. 10 68 0. 27 23s 0. 695 14 .04 27 0. 11 77 0. 31 235 0. 686 17 .04.

1 In Examples 2 and 3, coconut fatty acids were used as fatty acid 2 for ease of analysis and illustration. In Example 4, a mixture of 45% steam: and 55% palmitic acid was used as fatty acid 2.

1 Rati0=Weight of fatty acid per total weight of fatty acid-isethionate 1 and 2.

TABLE VI.ANALYSES OF FATTY ACIDS FOUND IN THE PRODUCT Fatty Active, Percent Free Acid, Percent Acid Total CNFA Emersol Total CNFA Erncrsol 2. 6 2. 6 0. 6 0. 6 G. 3 6. 3 3. 2 3. 2 39. 5 39. 5 33. 8 33. 8 l8v 5 18.0 19. l 18. 7 0. 4 l9. 5 10. 3 22. 8 9. 2 13.0

0. 5 0. 6 0. 4} 3 0 0. l. 1 0.1 Unk. O. 1 Stearie. 9.0 3. 2 5. 8 15.6 4. 0 11.6 Olcic 3. 7 3. 2 0.5 3. 7 3. 2 0. 5

=0. 08 (parts by weight).

=0. 28 (parts by weight).

It will be realized that the foregoing examples are for illustrative purposes only, and that many modifications and variations of the present invention may be derived. Accordingly, the invention is not to be limited to the specific embodiments illustrated.

We claim:

1. A method of preparing an ester of the formula RCOORSO M Where R is an aliphatic hydrocarbon having from 7 to 19 carbon atoms, R is selected from the group consisting of divalent hydrocarbon radicals containing from 2 to 4 carbon atoms and divalent aryl and alkylaryl radicals containing from 6 to 8 carbon atoms, and M is an alkali metal, comprising reacting a first acid of the formula R COOH, where R is an aliphatic hydrocarbon radical of 7 to 19 carbon atoms, said first acid including C to C acids, with a hydroxysulfonate of the formula HOR'SO M, R being as defined above, and continuing said reaction until the reaction is substantially completed, the effective ratio of said first acid to said hydroxy-sulfonate being between about 0.8 and about 1.1 moles per mole, and thereafter adding to the reaction mass a second acid of the formula R COOH, where R consists essentially of aliphatic hydrocarbon radicals of'13 to 19 carbon atoms, the total effective amount of said first and said second acids being at least about 1.2 moles per mole of hydroxy-sulfonate, and continuing said reaction until the reaction has substantially ceased.

2. A method of preparing an ester of the formula RCOORSO M, where R is an aliphatic hydrocarbon having from 7 to 19 carbon atoms, R is selected from the group consisting of divalent hydrocarbon radicals containing from 2 to 4 carbon atoms and divalent aryl and alkylaryl radicals containing from 6 to 8 carbon atoms, and M is an alkali metal comprising reacting a first acid of the formula R COOH, wherein R is an aliphatic hydrocarbon radical of 7 to 19 carbon atoms, said first acid containing a major amount of C to C acids and at least about 40% (l -C acids, with a hydroxy-sulfonate of the formula HOR'SO M, said reaction being carried to substantial completion in the presence of a reaction promoter and at a temperature between about 200 and about 240 C., the effective ratio of said first acid to said hydroxysulfonate being between about 0.8 and about 1.1 moles per mole, and thereafter adding to the reaction mass a second acid of the formula R COOH wherein R consists essentially of aliphatic hydrocarbon radicals of 13 to 19 carbon atoms, and continuing said reaction at a temperature between about 200 and about 240 C., until said reaction has substantially ceased, the total effective amount of said first and said second acids being at least about 1.2 moles per mole of hydroxy-sulfonate.

3. A method according to claim 2 wherein said first step is continued for a period of 30 to minutes.

4. A method according to claim 2 wherein said first acid is coconut fatty acid.

5. A method according to claim 2 wherein said second acid is tallow acid.

References Cited UNITED STATES PATENTS 3,029,264 4/1962 Alphen et a1 260400 NICHOLAS S. RIZZO, Primary Examiner.

J. H. TURNIPSEED, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,394,155 July 23, 1968 Arno Cahn et a1 It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

. Column 3, line 24, "uilization" should read utilization line 68, "0.10-0.17" should read 0.14-0.17 Column 4, line 5, "containings" should read containing line 18, "18 gms." should read 118 gms. Column 5, line 46, "micture" should read mixture Signed and sealed this 17th day of February 1970.

(SEAL) Attest:

Edward M. Fletcher, It. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

